Wednesday 28 September 2005 05.25 EDT
First published on Wednesday 28 September 2005 05.25 EDT

British scientists are set to go where only Bruce Willis has gone before: chasing after asteroids on a collision course with Earth. In a three-year £300,000 study funded by the government-backed Engineering and Physical Sciences Research Council, engineers will use computer simulations to work out the feasibility of changing the direction of asteroids.

"It's clear from geological records that the Earth has been impacted in the past by large objects," said Colin McInnes of Strathclyde University. Although none of the space objects currently tracked by Nasa are heading for Earth, Professor McInnes added that preparing for a potential catastrophe was a valid concern. "You have to place it in context - it's a small risk but with a high consequence."

The project will look at a range of methods proposed by scientists over the years, from giant mirrors floating in space which could vaporise parts of an asteroid to methods that rely more on brute force, such as smashing a rocket into the asteroid to deflect it.

"The deflection methods fall mainly in two categories, kinetic methods and low-thrust methods," said Gianmarco Radice of Glasgow University.

"Kinetic methods are those which provide an instantaneous change of properties within the asteroid. Sending a nuclear warhead or some sort of exploding device against the asteroid ... to create shock wave, for example. Low-thrust methods range from painting the surface of the asteroid with reflective or absorbing paint so that the properties of the surface are changed by attracting more or less light, thus heating or cooling the surface and changing the physical properties of the asteroid."

Whatever method is used, it would only change the path of the asteroid by minute amounts. "You can make very small adjustments to their orbits to create large changes in their orbits in the future," said Prof McInnes.

The exact methods used would have to vary depending on the type of asteroid being targeted. Some asteroids, known as rubble piles, are loose collections of rocks and ice. Slamming a rocket into these would be useless because the energy of the impact would just be absorbed, like the crumple zones in a car.

In this case, one method might mean melting part of the surface of the asteroid by concentrated sunlight. A large solar sail or mirror could reflect sunlight on to the surface of the asteroid and burn part of it away. The jets of gas produced would create a small but constant thrust that could deviate the asteroid into a new orbit.

More traditional solid asteroids have a range of options. "Another method is to place some sort of thrusting device on the surface of the asteroid," said Dr Radice. "It can either have its own fuel source, for example a solar power generator, which will create a very low thrust but over a longer period of time. Or you would have some sort of motor that uses the chemicals inside the asteroids to generate the fuel to work."

Alternatively, a spaceship could be launched and hurled directly into the asteroid. The idea would not be to physically push the asteroid away but to use the collision to gouge out a hole in the rock. The ejection of material would then push the asteroid in a different direction.

Meanwhile the European Space Agency (Esa) has already announced plans to conduct an experiment in deflecting asteroids away from the Earth.

Esa's Don Quijote mission will consist of two spacecraft: Hidalgo and Sancho. The former craft will smash into an asteroid named Apophis, which is expected to make its closest pass by the Earth in 2029, when it will be only 32,000km away.

The Sancho spacecraft will watch the collision and record any shift in the asteroid's trajectory. Esa plans to begin building Don Quijote in 2007, after a competition to select the best design from several European contenders.

Dodging disaster

Solar mirror

This would reflect light from the sun on to the asteroid to boil parts away. The stream of gases would move the asteroid out of the way of the Earth.

Paint

Covering the asteroid with paint or materials that either absorb or reflect light, heating or cooling bits and changing and way it moves.

Collision course

Smash a rocket or spacecraft into the asteroid to try to blow material away from the rock and change the asteroid's orbit.

Rockets

Land a rocket on the asteroid and use it to propel the rock in a different direction. Chemicals on the asteroid could be used.